In The Netherlands, the transit card create a great deal of budget. By having a digital card that you need to top up. You end up with money on a card that isn't used. Thus the transit company suddenly has €20-€50 extra cash available per train user. The intrest even generates pretty good money I can imagine

In the London Underground (and on the london buses) you can literally tap your contact-less debit or credit card. Just charged the cheapest rate for the route you took, which automatically caps per day or week on how much you pay, if you do multiple journeys, to be like an "all-day" or "all-week" pass.

Yup, I even got a refund the other day automatically. Not sure why as the tube wasn't really any worse than usual but hey, it was a free journey.

Surely that's mostly a one-off cash injection though? Once all the regular commuters have their cards, you're not going to get much more. There will still be some extra from visitors, and new commuters over time but it doesn't seem like long term you'd see that much revenue increase.

Don't forget tourists and other visitors. They buy cards with too much money and then never spend it. It is a constant source of revenue.

They can't do zone pricing with metrocard. Tap to enter and exit does.